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排序方式: 共有113条查询结果,搜索用时 15 毫秒
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A GEANT4-based Monte-Carlo (MC) model is developed to study the performance of endcap time-of-flight (ETOF) at BESⅢ. It's found that the multiple scattering effects, mainly from the materials at the MDC endcap, can cause multi-hit on the ETOF's readout cell and significantly influence the timing property of ETOF. A multi-gap resistive plate chamber (MRPC) with a smaller readout cell structure is more suitable for the ETOF detector due to significantly reduced multi-hit rate (per channel), from 71.5% for currently-used scintillator-based ETOF to 21.8% or 16.7% for MRPC-based ETOF, depending on the readout pad size used. The timing performance of an MRPC ETOF is also improved. These simulation results suggest and guide an ETOF upgrade effort at BESⅢ.  相似文献   
3.
We theoretically investigate the finite-temperature structure and collective excitations of a self-bound ultradilute Bose droplet in a flat space realized in a binary Bose mixture with attractive inter-species interactions on the verge of meanfield collapse. As the droplet formation relies critically on the repulsive force provided by Lee–Huang–Yang quantum fluctuations, which can be easily compensated by thermal fluctuations, we find a significant temperature effect in the density distribution and collective excitation spectrum of the Bose droplet. A finite-temperature phase diagram as a function of the number of particles is determined. We show that the critical number of particles at the droplet-to-gas transition increases dramatically with increasing temperature. Towards the bulk threshold temperature for thermally destabilizing an infinitely large droplet, we find that the excitation-forbidden, self-evaporation region in the excitation spectrum, predicted earlier by Petrov using a zero-temperature theory, shrinks and eventually disappears. All the collective excitations, including both surface modes and compressional bulk modes, become softened at the droplet-to-gas transition. The predicted temperature effects of a self-bound Bose droplet in this work could be difficult to measure experimentally due to the lack of efficient thermometry at low temperatures. However, these effects may already present in the current cold-atom experiments.  相似文献   
4.
姬小建  陈明文  徐小花  王自东 《中国物理 B》2015,24(1):16401-016401
The growth behavior of a columnar crystal in the convective undercooled melt affected by the far-field uniform flow is studied and the asymptotic solution for the interface evolution of the columnar crystal is derived by means of the asymptotic expansion method.The results obtained reveal that the far-field flow induces a significant change of the temperature around the columnar crystal and the convective flow caused by the far-field flow accelerates the growth velocity of the interface of the growing columnar crystal in the upstream direction and inhibits its growth velocity in the downstream direction.Our results are similar to the experimental data and numerical simulations.  相似文献   
5.
为了掌握微通道板探测器的X射线脉冲信号观测能力,利用X射线脉冲星地面实验装置,开展了长时间的不同流强和不同背景噪声强度下的微通道板探测器脉冲信号探测实验,并建立了一套X射线探测器脉冲观测能力评估方法,推导出基于光子计时模式下X射线探测器的脉冲信号信噪比、脉冲轮廓相似度、脉冲到达时间精度和最小可探测功率的关系表达式.实验中,利用面积20cm~2的微通道板探测器开展了8组10 000s的实验,采集到有效观测数据,然后搜索最佳脉冲周期,重构观测脉冲轮廓,估计脉冲轮廓特征参数.实验表明,微通道板探测器具备良好的X射线脉冲信号观测与恢复能力,在较弱脉冲信号强度(光子流量密度为0.05ph/cm~2/s)和较强背景噪声(背景噪声强度是脉冲信号的16倍)下获取观测脉冲轮廓的信噪比、相似度、脉冲到达时间观测精度分别为35.73、88.38%、51.53μs和64.89、89.72%、29.24μs,验证了微通道板探测器具备一定的暗弱X射线脉冲星观测能力,且微通道板探测器的脉冲探测能力随着脉冲信号强度增加、背景噪声强度减弱、累积观测时间增加而提升.  相似文献   
6.
以滤纸为基底材料,通过滴涂导电碳浆及Ag/Ag Cl浆,分别制备了固态聚合物膜钙离子选择性指示电极和固态聚合物膜参比电极,构建了纸芯片离子选择性电极系统,用以检测海水中Ca~(2+)。实验中,优化了离子载体含量与离子选择性敏感膜厚度,考察了参比电极的稳定性及指示电极的选择性。结果表明,在0.5 mol/L NaCl背景下,该系统在1.0×10-4~3×10-2mol/L范围内呈现线性响应,响应斜率为24.3 m V/dec。将纸芯片电极用于实际海水样品中Ca~(2+)含量的测定,所得结果与电感耦合等离子体-原子发射光谱法检测数据一致。  相似文献   
7.
Considering the spin degree of freedom of the Dirac field, we study the entanglement behavior of a different class of communication channel and teleportation of three-dimensional single particle state in noninertial frames. Numerical analysis shows that the communication channel in our scheme can offer enough distillable entanglement for the teleportation protocol. Moreover, the teleportation protocol could work well if Rob's acceleration is not very big, but the fidelity of the teleportation is still reduced due to the Unruh effect.  相似文献   
8.
Ag掺杂型空心TiO2纳米微球的制备与表征及其光催化性能   总被引:1,自引:0,他引:1  
通过甲基丙烯酸与苯乙烯的乳液聚合制备了表面载有阴离子的聚苯乙烯(PSt)纳米乳胶粒. 在乙醇与水的混合溶剂中, 用硅烷偶联剂乙烯基三甲氧基硅烷对其进行表面改性. 以此乳胶粒为模板, 加入钛酸四丁酯和硝酸银制备了Ag2O掺杂型聚苯乙烯/二氧化钛(PSt/TiO2)复合微球. 对该微球在180 °C进行液相预处理、干燥、500 °C煅烧等步骤制备了Ag 掺杂型Ag-TiO2复合粒子. 通过扫描电镜(SEM)、透射电镜(TEM)和X射线衍射(XRD)等手段对PSt/TiO2复合粒子及Ag-TiO2空心粒子的形貌及晶体结构等进行了表征. 考察了Ag-TiO2复合粒子在紫外光(365 nm)与紫外-可见光(370-760 nm)下对罗丹明B (RhB)降解的催化活性. 结果表明, 与不含银的TiO2空心微球相比, 在紫外光照射下, 银含量(nAg/nTi)为0.1%的Ag-TiO2复合粒子对RhB的降解率提高了11%左右; 在紫外-可见光照射下, nAg/nTi为1.0%和2.0% 的Ag-TiO2复合粒子对RhB的降解率提高了30%左右.  相似文献   
9.
以多环芳烃作为变量,建立了原油、燃料油属性鉴别的费谢尔判别法。分别测定了来自不同国家和地区的26个原油样品和25个燃料油样品中8种多环芳烃的含量,并将它们作为判别变量。借助SPSS 16.0进行费谢尔判别分析,建立费谢尔判别函数。将未知样品的判别变量值代入后,可以快速地得知样品的类别。结果表明,以多环芳烃作为判别变量进行原油、燃料油费谢尔判别快速而准确。  相似文献   
10.
This paper reports that the organic field-effect transistors with hybrid contact geometry were fabricated,in which the top electrodes and the bottom electrodes were combined in parallel resistances within one transistor.With the facility of the novel structure,the difference of contact resistance between the top contact geometry and the bottom contact geometry was studied.The hybrid contact devices showed similar characteristics with the top contact configuration devices,which provide helpful evidence on the lower contact resistance of the top contact configuration device.The origin of the different contact resistance between the top contact device and the bottom contact device was discussed.  相似文献   
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